Drought stress is a serious problem that affects many regions of the world, decreasing productivity worldwide. Drought stress implies lack of water partially or completely which in turn leads to decreased crop yield. Growth and photosynthesis are two of the most important processes affected by water stress (Kramer and Boyer, 1995) and happen to be major causes of decreased crop yield. On a global basis, it is a major cause limiting productivity of agricultural systems and food production (Boyer 1982). In cereal crops, which provide the major carbohydrate staples for humans, even intermittent water stress at critical stages may result in considerable yield reduction (Ludlow and Muchow 1990) and crop failure. Subbarao et al. 1995 suggested that production could be increased over present levels in chick pea, pigeon pea and ground nut by 49%, 57% and 29% respectively if water was not a limiting factor Water deficit is also the most important abiotic stress affecting rice production. In Asian uplands water deficit results in an estimated average annual loss of 190 kg/ha or 17% of the production (Edmeades et al. 2001). Irrigated rice loses 134 kg/ha due to shortages of water or 9.9 million tones of grain annually in Asia. These losses are expected to increase in future as water scarcity in Asia becomes more severe.
The primary physical effect of drought or dry soil conditions is direct damage to the roots and root death. Drought can lead to cellular desiccation, which in turn leads to osmotic stress. While all plants respond at molecular and cellular levels leading to physiological changes and some level of drought tolerance, some plants show more drought tolerance than others. The cellular response towards osmotic stress is the production of osmoprotectants like, proline, glycine betaine and dimethyl sulfonium compounds. One of the plant hormones that is induced by drought stress and is well documented in literature is abscisic acid (Shinozaki, K and Yamaguchi-Shinozaki, K. et al., 1997). ABA is produced under water deficit conditions and plays an important role in tolerance against drought. Most of the drought inducible genes that have been studied to date are induced by ABA (Shinozaki, K and Yamaguchi-Shinozaki et al., 1996).
Plant cells are continuously stressed by toxic reactive oxygen species (ROS) generated by the consumption of oxygen during metabolic respiration and by the production of oxygen during photosynthesis. When plants are exposed to stresses such as pathogen attack, high salt, mechanical damage, drought and chilling, large amount of ROS are generated (Holland et al., 1993, Kuroda et al., 1992, Levine et al., 1994). These toxic ROS consist of singlet oxygen, superoxide radicals, hydrogen peroxide and hydroxyl radicals. When they accumulate in a plant cell, an oxidative burst may occur to destroy the cell. However, the plant cells are normally protected from such oxidative damage by removing the ROS by enzymes such as superoxide dismutase, catalase and peroxidase. Scavenging of ROS by free radicals such as carotenoids, tocopherol, ascorbate and glutathione represents another mechanism for anti-oxidation.
Soluble Glutathione-S-transferases (GST-EC 2.5.1.18) are a family of multifunctional dimeric enzymes that catalyzes the nucleophilic attack of the tripeptide glutathione on lipophilic compound with electrophic centers. The primary function of GSTs is generally considered to be detoxification of both endogenous and xenobiotic compounds (Marrs 1996, Amstrong 1997, Hyes and McLellan 1999). The vital role of GST is supported by their ubiquitous occurrence in eukaryotes and prokaryotes. Besides the formation of glutathione conjugates, GST can also catalyze isomerisation reactions, act as glutathione peroxidases and serve as binding and possibly transport proteins (ligandins) for lipophilic compounds (Edwards et al. 2000).
Prosopis juliflora, commonly known as mesquite or Vilayathi Babul is a thorny evergreen to semi-evergreen fast growing tree belonging to the family Fabaceae and capable of withstanding extended periods of drought. The moisture requirement for growth is low and it can survive in areas where the water table is lower than 30 m and rainfall is about 70 mm (Kelvin R. Hultine). The minimum daytime water potential a plant can tolerate is a measure of its drought tolerance; Prosopis juliflora can withstand water potential of −4.8 mega Pascals or below (Nilsen et al. 1981). This remarkable feature of drought tolerance by this species makes it is a good source material for identification and isolation of drought tolerant genes. Developing drought tolerant crop plants could reduce the economical loss due to drought stress. The above documents do not suggest or teach the present disclosure.